1. Field of the Invention
The present invention relates to improvements made to gas flowrate measuring and monitoring devices, in particular devices with low flowrates.
2. Description of the Prior Art
Certain known devices use the deformation of two deformable chambers supplied with the same gas pressure higher than atmospheric pressure, to measure and monitor the gas flowrate.
In these devices, one of the chambers is supplied with said gas pressure through a flowrate restriction device, the flowrate of which is substantially the same order of magnitude as that to be measured. Moreover, this chamber can be placed in communication with the ambient atmosphere and hence with atmospheric pressure when the device is in the resting position, and in communication with the system of which the flowrate is to be measured, when the device is in the measuring position.
In the resting position, the pressure prevailing in the first chamber is the supply pressure, and the pressure in the second chamber is close to atmospheric pressure.
In the measuring position, the pressure prevailing in the first chamber remains equal to the supply pressure, and the pressure in the second chamber increases up to a value slightly less than the supply pressure; the difference in pressure results from the pressure loss experienced by the gas flow as it passes through the system whose flowrate is to be measured and hence depends on the flowrate of the latter.
Thus, it is the difference in pressure between the two chambers that enables the flowrate to be monitored to be measured and, for this purpose, deformation of these chambers is detected, which deformation can be amplified in any fashion--mechanically, electronically, or otherwise.
The drawback of this type of device resides in the fact that it has a relatively long response time, which is inherent in its very design, since the pressurized gas passes into the second chamber at the time of measurement through the flowrate restriction device. If a more precise measurement were to be made, the flowrate of the restriction device would have to be decreased by comparison with the flowrate to be measured, which would extend the response time even longer, while to cut down the response time a restriction device with a higher flowrate than the flowrate to be measured would have to be provided, in which case measurement would be less accurate.